This invention relates generally to sheet feeding and separating apparatus, and more particularly, to compositions for the surfaces of sheet feeding and separating apparatus to improve serially feeding superposed sheets from a stack of sheets to a xerographic machine. The invention further relates to compositions for the surfaces of sheet retarding devices in paper handling systems.
The development of high speed xerographic machines has brought about the need for simple yet reliable document feeder and separator apparatus capable of handling documents (sheets) varying in length, width, thickness, weight, and surface conditions. In order to serve in a wide variety of applications these same machines require that the feeder and separator apparatus operate efficiently and reliably both as an automatic feed on the one hand and as a manual input feeder on the other hand.
For example, in the automatic sheet feeder and separator apparatus of the type disclosed in U.S. Pat. No. 3,469,834 issued to Stange, Lux and Michaels and U.S. Pat. No. 3,768,803 issued to Stange, there are described means for advancing and separating superposed sheets having varied physical characteristics comprising various types of retarding members having frictional resistivity surfaces thereon to cause good sheet separation of the superposed sheets stacked in a holder for feeding into a xerographic machine. The separation belt and retard member are employed in these patents for queuing and advancing the sheets and/or separating them from the stack. In these patents, the region of contact between the retarding member and the separation belt form a sheet queuing throat which is able to "fan out" or queue sheets passed through it. In U.S. Pat. No. 3,768,803 the separation belt and retard member are positioned adjacent the edge of a stack of sheets, and the sheets translate a very short distance before reaching a sheet queuing throat because the retard member is positioned close to the edge of the stack.
In the above-cited references and in retard or retarding members in general, the retard member may assume various shapes, sizes, thicknesses, and configurations, including rolls, belts, endless belts, shoes, pads, and the like. In U.S. Pat. No. 3,469,834 the retarding roll or abutment member has a frictional member thereon which is formed of a resilient material having a lower coefficient of friction than that of the separator feed belt, said resilient material being mounted on a retarding roll or abutment member in alignment and engagable with the separator feed belt. In U.S. Pat. No. 3,768,803 the retard surface is preferably a soft rubber of about 40 durometer rating. This resiliency or softness permits the lead edge of the sheets to "dig into" the retard means. The retard means should not be too soft, however, or wear will be excessive. For this reason, it is suggested that the retard means be grooved to give it mechanical softness, resiliency or flexibility while the durometer of the material is high to minimize wear. Thus, the shortcomings of the retard surfaces of the prior art retard members are a high wear rate when the retard surface is of a soft, rubber material. When the hardness or durometer rating of the retard surface is high to minimize the wear of the surface, the resulting effect on the paper is lead edge delamination. Accordingly, a decrease in retard wear rate implies an increase in lead edge delamination of the sheets. Furthermore, decrease in hardness of the retard surface also results in sheet multifeeds.